Electrical feed-screw type linear actuators for sick beds/nursing beds, raise and lower the bed or tilt the back section or knee section of the bed in order to lower the burden on patients of living daily.
Technology for linear actuators of this type in the background art is disclosed in the patent document 1.
Namely, this linear actuator contains a shaft with a male screw, a worm reduction gear for reducing and transmitting the rotation of the motor to the shaft, a female screw member (feed nut) that is coupled by a screw to the male screw of the shaft and advances and retreats by the rotation of the shaft, a moving cylinder that is fixed to the female screw member and advances and retreats relative to a housing, and a potentiosensor for detecting the position of the moving cylinder. This linear actuator is structured so that the moving cylinder is connected by way of a coupling piece to a link to move the bed up and down or to tilt the back section or knee section of the bed while the potentiosensor detects the position of the moving cylinder.
In some cases, the sick bed/nursing bed is equipped with equipment called a CPR mechanism.
The CPR mechanism is a device for making the bed return to a flat state in emergencies such as requiring cardio-pulmonary resuscitation.
This CPR mechanism must operate quickly and reliably whatever the circumstances, and must not restrict the operations of the linear actuator in a normal use of bed.
The technology in the patent document 2 discloses a sick bed/nursing bed containing this type of CPR mechanism.
In this type of sick bed/nursing bed, a cable joins an operating lever installed on the rear side of the back recliner plate to a release lever for canceling the operation of the anti-reverse mechanism in the linear actuator. This mechanism allows easily rotating the release lever in the release direction by gripping the operating lever to temporarily raise the back recliner plate in order to release the load acting on the anti-reverse mechanism.
The linear actuator containing CPR mechanism also includes mechanisms where pushing an operating lever shifts the operating rod of a one-way clutch to automatically disengage the one-way clutch (see the patent document 3).
Patent document 1: Japanese Patent Non-Examined Publication No. 2005-188571
Patent document 2: Japanese Patent Non-Examined Publication No. 2003-52762
Patent document 3: Japanese Patent Non-Examined Publication No. 2000-253618